The present invention relates to a film and a film-forming composition therefore. More specifically, the invention relates to an insulating film which is adapted for use in electronic devices such as semiconductor devices, has good film properties such as dielectric constant and mechanical strength, and can be formed as a coat of suitable and uniform thickness. The invention further relates to an electronic device made using such an insulating film.
Recently, in the field of electronic materials, advances in the levels of integration, functionality and performance have led to increases in circuit resistance and capacitance between interconnects, and to increases in power consumption and delay time. Of these, because an increase in the delay time lowers the signal speed of devices and leads to crosstalk, a lower parasitic resistance and a lower parasitic capacitance are desired in order to shorten the delay time and thus increase the speed of the device. One specific approach for lowering the parasitic capacitance currently being tried is to cover the periphery of the interconnects with an insulating film (also referred to herein as an “interlayer dielectric”) having a low dielectric constant.
It is desired that such an interlayer dielectric have an excellent heat resistance capable of withstanding the thin-film forming operation during mount board production and subsequent operations such as chip connection and pin attachment, and that it have a chemical resistance capable of withstanding wet processes. Moreover, in recent years, increasing use is being made of low-resistance copper interconnects in place of aluminum interconnects; with this transition, planarization using a chemical mechanical polishing (CMP) process has become commonplace. A high mechanical strength capable of withstanding the CMP process is thus desired.
A number of resin compositions for forming interlayer dielectrics have already been described in the art. For example, JP 2002-534546 A discloses a highly heat-resistant insulating film made of a high heat-resistance resin in which the basic backbone structure is a polyarylene ether. In addition, JP 2004-504455 A discloses thermoset monomers such as diadamantane monomers substituted with aryl groups and carbon-carbon triple bonds. Moreover, resins constructed of such monomers are described as forming materials having a low dielectric constant. Yet, to achieve high-speed devices, it is desirable that the dielectric constant be lowered even further.
One method that is known for achieving a lower dielectric constant involves adding a pyrolyzable compound to a dielectric film so as to form pores and thereby lower the dielectric constant. Yet, although the greater porosity does result in a lower dielectric constant, such porous films have a number of drawbacks, including a lower mechanical strength and a susceptibility to increases in dielectric constant owing to moisture adsorption. Because materials which fully satisfy the desired qualities, including the low dielectric constant and good mechanical characteristics required of an insulating film, have not previously been found, there has been a need for further improvements.
Silica (SiO2) films formed by vacuum processes such as chemical vapor deposition (CVD) have until now been frequently used as insulating films and films for optical applications. In addition, coating-type insulating films referred to as spin-on-glass (SOG) films which are composed primarily of a product of tetraalkoxysilane hydrolysis have recently come into use, primarily in order to achieve more uniform interlayer dielectrics. Also, the increasing level of semiconductor device integration has led to the development of what are known as organic SOG films—interlayer dielectrics having a low dielectric constant which are composed primarily of polyorganosiloxane.
However, films composed of inorganic materials generally do not have a very low dielectric constant. SiOF films recently investigated as low-dielectric CVD films have a relative dielectric constant of about 3.3 to 3.5. Yet, such films have a high moisture absorption, as a result of which the dielectric constant rises in the course of use.
In view of the above, methods are known for adding a high-boiling solvent or a pyrolyzable compound to an organopolysiloxane as an insulating film material having excellent insulating properties, heat resistance and durability, and thereby forming pores so as to lower the dielectric constant. However, in such porous films, although forming numerous pores does lower the dielectric constant, a number of problems arise, such as a decline in mechanical strength and a susceptibility to increases in the dielectric constant due to moisture absorption. Another problem is that, owing to the formation of mutually interconnected pores, the copper that has been used in the interconnects diffuses into the insulating film.
An attempt to obtain a film having a low refractive index and a low density by coating a solution prepared by adding a low-molecular-weight cage compound to an organic polymer is also known (see JP 2000-334881 A). However, the addition of a cage compound monomer fails to provide adequate refractive index and dielectric constant-lowering effects. Other drawbacks of this approach include a deterioration in the state of the coated surface and film loss during baking. Because materials which fully satisfy the desired qualities, including the low dielectric constant and good mechanical characteristics required of an insulating film, have not previously been found, there has been a need for further improvements.